Petroleum refineries have need to dispose of wastes comprised of oily sludges (oil-solid or oil-solid-water mixtures) produced in wastewater treatment facilities and hydrocarbon storage tanks. Most of these wastes are considered biodegradable and can be disposed of at landtreatment sites. Landtreatment (landfarming) is a low cost disposal method for such wastes. However, certain types of oily sludges cannot be landtreated due to the biorefractory nature of the oil contained therein. For example, some refinery tank bottom sludges (e.g., coker hot slop tank sludge and cat fractionator bottoms sludge) contain viscous oil and high levels of biorefractory polynuclear aromatic components, which are not suitable for disposal through landtreatment. Removal of biorefractory oil from oily sludges in order to make them suitable for landtreating could be an attractive waste management option. However, conventional deoiling processes and services are costly and in some cases do not achieve the desired result. For example, extraction-based technologies using high hydrocarbon gases (C.sub.3 to C.sub.5) and special solvents rely on recovery and recycle of the solvent, and may leave asphaltene fractions of the oil on the solids.
It is therefore an object of the present invention to provide a flexible low cost process for rendering waste oily sludges suitable for landtreatment. Alternatively, some kinds of sludges may be rendered usable, for example, sludges composed of coke fines can be converted into solid fuel material. It is a further object of the invention to be able to handle oily sludges containing biorefractory and/or asphaltenic oil fractions. It is a still further object to displace any biorefractory oil in the sludge with a biodegradable oil.
The prior art discloses various processes for treating oily sludges. U.S. Pat. No. 3,696,021 to Cole et al. discloses mixing an oily sludge with light hydrocarbons passing through a conduit. Solids, water and oil are separated in a drum. The oil is heated in a vessel and distilled in a tower to separate heavy oil and recirculate the light oil. The solids are used for landfill.
U.S. Pat. No. 4,014,780 to McCoy mixes an oily sludge with a diluent recycle oil and heats the mixture with steam to recover the oil and form dry solids for a landfill. U.S. Pat. No. 4,097,378 to St. Clair discloses mixing sludge with oil and then treating the same with recycle oil. U.S. Pat. No. 4,264,453 to Mraovich discloses filtering coke from oil wastes mixed with a diluent oil. U.S. Pat. No. 4,686,048 to Atherton et al. prepares sludge fines for a landfill by mixing the sludge with a hydrocarbon diluent.
U.S. Pat. No. 4,264,453 addresses the treatment of coal tar wastes and uses a non-aromatic diluent with surfactants to render the wastes (coke fines, viscous oil, water) amenable to separation by filtration. U.S. Pat. No. 3,696,021 uses butane, pentane or their mixture as a solvent and requires a high temperature (300.degree.-400.degree. F.) and a high pressure (500-600 psig) separation of solvent from waste oil. U.S. Pat. No. 4,686,048 uses a hydrocarbon type solvent having a boiling point when mixed with water of less than 212.degree. F. In addition, it requires mixing of filtered cake with 100% to 1500% water, and distilling the mixture to remove the residual solvent from the solids.
Various patents disclose combining a waste sludge with a refinery stream. U.S Pat. No. 4,206,001 discloses a process for separating solid and liquid materials in an FCC rundown tank to permit liquids to be returned to refinery process streams. The process comprises the addition of a selected refinery stock, preferably kerosene-like, into the rundown tank, followed by washing of solids with an aqueous solution, and subsequent settling to separate the aqueous and organic phases. U.S. Pat. No. 2,487,103 teaches adding a heavy naphtha fraction to sludge, followed by addition of water for hydrolysis and phase separation. U.S. Pat. No. 3,696,021 discloses mixing refinery sludges with light hydrocarbons to deoil the solids, followed by gravitational separation and steaming of the separated solids to remove the light hydrocarbons. Other patents in this area include U.S. Pat. No. 2,413,310; U.S. Pat. No. 3,079,326; U.S. Pat. No. 1,092,386; and U.S. Pat. No. 1,092,386.